Seo Il Chang

Amplitude Modulated Dynamics of a Resonantly Excited Autoparametric Two Degree-of-Freedom System

Forced, weakly nonlinear oscillations of a two degree-of-freedom autoparametric vibration absorber system are studied for resonant excitations. The method of averaging is used to obtain first-order approximations to the response of the system. A complete bifurcation analysis of the averaged equations is undertaken in the subharmonic case of internal and external resonance. The “locked pendulum” mode of response is found to bifurcate to coupled-mode motion for some excitation frequencies and forcing amplitudes. The coupled-mode response can undergo Hopf bifurcation to limit cycle motions, when the two linear modes are mistuned away from the exact internal resonance condition. The software packages AUTO and KAOS are used and a numerically assisted study of the Hopf bifurcation sets, and dynamic steady solutions of the amplitude or averaged equations is presented. It is shown that both super-and sub-critical Hopf bifurcations arise and the limit cycles quickly undergo period-doubling bifurcations to chaos. These imply chaotic amplitude modulated motions for the system.

Non-Linear Vibrations and Chaos in Harmonically Excited Rectangular Plates with One-to-One Internal Resonance

Nonlinear flexural vibrations of a rectangular plate with uniform stretching are studied for the case when it is harmonically excited with forces acting normal to the midplane of the plate. The physical phenomena of interest here arise when the plate has two distinct linear modes of vibration with nearly the same natural frequency. It is shown that, depending on the spatial distribution of the external forces, the plate can undergo harmonic motions either in one of the two individual modes or in a mixed-mode. Stable single-mode and mixed-mode solutions can also coexist over a wide range in the amplitudes and frequency of excitation. For low damping levels, the presence of Hopf bifurcations in the mixed-mode response leads to complicated amplitude-modulated dynamics including period doubling bifurcations, chaos, coexistence of multiple chaotic motions, and crisis, whereby the chaotic attractors suddenly disappear and the plate resumes small amplitude harmonic motions in a single-mode. Numerical results are presented specifically for 1 : 1 resonance in the (1, 2) and (3, 1) plate modes.

Modeling of road traffic noise and estimated human exposure in Fulton County, Georgia, USA.

Environmental noise is a major source of public complaints. Noise in the community causes physical and socio-economic effects and has been shown to be related to adverse health impacts. Noise, however, has not been actively researched in the United States compared with the European Union countries in recent years. In this research, we aimed at modeling road traffic noise and analyzing human exposure in Fulton County, Georgia, United States. We modeled road traffic noise levels using the United States Department of Transportation Federal Highway Administration Traffic Noise Model implemented in SoundPLAN®. After analyzing noise levels with raster, vector and façade maps, we estimated human exposure to high noise levels. Accurate digital elevation models and building heights were derived from Light Detection And Ranging survey datasets and building footprint boundaries. Traffic datasets were collected from the Georgia Department of Transportation and the Atlanta Regional Commission. Noise level simulation was performed with 62 computers in a distributed computing environment. Finally, the noise-exposed population was calculated using geographic information system techniques. Results show that 48% of the total county population [N=870,166 residents] is potentially exposed to 55 dB(A) or higher noise levels during daytime. About 9% of the population is potentially exposed to 67 dB(A) or higher noises. At nighttime, 32% of the population is expected to be exposed to noise levels higher than 50 dB(A). This research shows that large-scale traffic noise estimation is possible with the help of various organizations. We believe that this research is a significant stepping stone for analyzing community health associated with noise exposures in the United States.

Transportation noise and exposed population of an urban area in the Republic of Korea

Using noise prediction models, we explored the transportation noise levels of Youngdeungpo-gu, an urbanized area of Seoul Metropolitan City in the Republic of Korea. In addition, we estimated the population exposed to transportation noise levels and determined how many people are vulnerable to noise levels that would cause serious annoyance and sleep disturbance. Compared with the World Health Organization [WHO] recommended levels, the daytime and nighttime transportation noise levels were still high enough to have the two psychosocial effects on people when considering the recommended levels of the World Health Organization (WHO; 55 decibels [dB[A]] and 40 dB[A] for daytime and nighttime, respectively). Particularly, nighttime transportation noise was discovered to be harmful to a wider area and more people than daytime noise. Approximately 91% of the Youngdeungpo-gu area experienced nighttime transportation noise levels exceeding those recommended by WHO. It was estimated that as much as 80% of the people in the study area were exposed to transportation noise levels >40 dB[A] during nighttime. Taking this into account, there is an urgent need to control and reduce transportation noise levels in Seoul, to protect residents against the potential ill health effects caused by urban transportation.

Subharmonic responses in harmonically excited rectangular plates with one-to-one internal resonance

Abstract Non-linear flexural vibrations of a rectangular plate with uniform stretching are studied for the case when it is subharmonically excited at nearly three times one of the linear natural frequencies. The interest here is in the subharmonic response of the plate when two distinct linear modes are near one-to-one internal resonance. Using the method of averaging, it is shown that, depending on the spatial distribution of the external forces, the plate can undergo harmonic motions, subharmonic motions in the directly excited spatial mode, or subharmonic motions in which both the internally resonant modes participate. The coupled-mode subharmonic oscillations can also undergo Hopf bifurcation to complicated amplitude-modulated subharmonic solutions which exhibit period-doubling route to chaos. Numerical results are presented specifically for one-to-one resonance in the (1,2) and (3,1) plate modes. The two-mode discretization of the von Karman plate equations are also directly simulated to verify some of the predictions of the averaged equations.

Excess Noise Map for Environmental Standard and Assessment of Noise with Using GIS Data

Using GIS data of C-si as basic data when making noise map of road traffic, we estimated exactly the noise excess areas and consequently suggested the population and the area exposed to road traffic noise accurately. We made 3D noise map to assess regional distribution of noise quantitatively. The noise map consists of noise prediction model based on data base such as traffic volume and speed changes for estimating quantitatively the noise and 3D urban space model which includes locations of noise sources, 3D buildings, topography and roads. We made noise standard map according to land use conditions and compared this map to road traffic noise map, and consequently made excess noise map. Using excess noise map, we assessed areas which exceed environmental noise level standards and noise guidelines quantitatively and effectively through GIS spatial analysis, and consequently more accurate noise exposed area and noise exposed population could be estimated. To show buildings` outer walls noise exposure, we analyzed 3D urban noise distributions using 3D-analysis of GIS.

A Study on Sampling Techniques to Assure the Representativeness of Short-term Equivalent Noise Level

The purpose of this study is to present a guideline to design a short-term manual measurement of environmental noise level, which is more economical and flexible, but less representative than long-term automatic measurement. The proposed guideline can provide the number of measurement times and the length of measurement term required to secure the extent of the representativeness. The data was collected at 4 sites located in Seoul and at 4 sites located outside of Seoul. The probabilities for five-minute equivalent noise levels, Leq, 5min, to stay in an error range from the quarterly representative noise level were used to evaluate sampling techniques. The probability analysis of the daytime period showed that the noise levels measured between 10 am and 2 pm and between 9 pm and 10 pm have the probabilities higher than 60 %. On the other hand, even for the same length of total measurement time, increasing the number of random samplings results in higher probabilities than increasing the length of measurement term.

Application Method of Logistic Regression Analysis for Annoyance Prediction Model Based on Predicted Noise Level

ABSTRACT Predicted noise level has been used to assess the annoyance response since noise map was generalized and being the normal method to assess the environmental noise. Unfortunately using predicted noise level to derive the annoyance prediction curve caused some problems. The data have to be grouped manually to use the annoyance prediction curve. The aim of this paper is to propose the method to handle the predicted noise level and the survey data for annoyance prediction curve. This paper used the percentage of persons annoyed(%A) and the percentage of persons highly annoyed as the descriptor of noise annoyance in a population. The logistic regression method was used for deriving annoyance prediction curve. It is concluded that the method of dichotomizing data and logistic regression was suitable to handle the predicted noise level and survey data. * 1. 서 론 소음에 대한 어노이언스 예측모델 수립을 위한 연구는 몇 십년 전부터 유럽을 중심으로 지속적으로 수행되어져 왔다 (1~4) . 최근에는 유럽뿐만 아니라 다양한 국가에서 환경 소음에 대한 어노이언스 예측모델 수립을 위한 연구를 지속하고 있으며 우리†교신저자; 정회원, 서울시립대학교 환경공학부E-mail : schang@uos.ac.krTel : (02) 2210-2177, Fax : (02)2210-2877* 정회원, 서울시립대학교 환경공학과** 서울시립대학교 도시사회학과*** 정회원, 한국환경정책평가연구원# 이 논문의 일부는 2010년 춘계 소음진동 학술대회에서발표되었음.나라도 예외가 아니다

Sound grade classification with sound mapping of national park trails in South Korea

Most of the national parks in South Korea are exposed to noise pollution caused by urban noise from adjacent cities. Especially, the road-traffic noise from the roads passing through or surrounding the parks has increased the exposure. In addition, the military and tele-communication facilities located in ecologically sensitive highlands are noise sources and affect nearby ecosystems. Therefore, it is important to preserve and maintain a comfortable sound environment to ensure the quality of the park trails for visitors and the habitat of animals and plants. The purpose of this study is to map a sound environment of national parks in South Korea and to classify sound grades of park trails. The park trails were categorized into 5 different groups based on acoustic factors such as noise level, loudness, sharpness, roughness, and tonality, and environmental factors such as land-use, ground coverage, vegetation type, and relative location which can be obtained from biotope map and GIS DB. This classification was based on factor analysis and cluster analysis. It is expected that this sound grade classification of the national park trails meets the right of visitors to know the sound environment, and that the managers of national parks can use it as a guideline to create a positive sound environment.

Who is the bigger culprit? Studying impacts of traffic and land use on noise levels in CBD area of Karachi, Pakistan

The trend of urbanization has attracted increased attention towards urban areas around the world. Central business districts (CBDs) serve as the core of commercial activities of urban areas and are often associated with high-density population. Noise pollution in urban areas, especially CBDs, is considered as an important issue for planners and policy makers especially with regard to human health. Noise prediction models for CBD area of Karachi, Pakistan, have been developed in this study using land use and traffic parameters. These models show that traffic and built-up space (especially residential land use) contribute positively and vacant space contributes negatively to the noise levels. However, it was found that traffic volume has higher impact, than land use, in terms of on noise levels in CBD area. The models of this research are anticipated to be used for planning of urban CBD areas in other cities where noise levels do not meet international health standards. In addition, they would be useful in calculating the rate of traffic volume associated with residential land use.